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INFLUENCE OF CERTAIN" ELEMENTS ON STEEL.               35&
car wheels, dredger links and rpins, and other: articles where. the maximum of hardness must be combined with toughness. Its great disadvantage is the difficulty of doing machine work upon it, for the best of hardened tools will rapidly crumble and wear out. In cases where finishing is essential it is necessary to grind by emery wheels.                                    .,                                           , ;
SEC. XVIId.—Influence of sulphur.—Nothing is better established than the-fact that sulphur injures the rolling qualities of steel, causing it to crack and tear, and, lessening its capacity to •weld. The critical content at which the metal ceases to be malleable and weldable varies with every steel. It is lower with each increment of copper, higher with each unit of manganese, and lower in steel which has been cast too hot. In the making of steel for simple shapes, a content of .10 per cent, is possible, and may be exceeded if care be taken in the heating, but for rails and other shapes having 'thin flanges it is advantageous to have less than .08 per cent., while every decrease below this point is seen in a reduced number of de-. fective bars. It is impossible to pick out two steels with different contents of sulphur and say that the influence of a certain minute quantity can be detected, but it is none the less true that the effect of an increase or decrease of .01 per cent, will show itself in the long run, while each .03 per cent, will write its history so that he who runs may read.
The effect of sulphur upon the cold properties of steel has not been accurately determined, but it is certain that it is unimportant. In common practice the content varies from .OB to .10 per cent., and within these limits it has no appreciable influence upon the elastic ratio, the elongation, or the reduction of area. It is more difficult to say that it does not alter the tensile strength, for a change of one thousand pounds per square inch, can be caused by many things. Webster* has stated that sulphur probably increases the ultimate strength at the rate of 500 pounds per square inch for every .01 per cent., but I am inclined to think his conclusion is not founded on sufficient premises. In rivets, eye-bars and firebox steel, the presence of sulphur is objectionable, for it creates a coarse crystallization when the metal is heated to a high temperature, and reduces the toughness of the steel, In other forms of
* Further Observations on the Relations between the Chemical Constitution and Physical Character of Steel.   Trans. A. I. M. JS?., Vol. XXIII, p, 113.